You could always simply tell the hostess you are under a time crunch as he/she is taking you to your table, and then tell the waiter the same thing. Also, be ready to order as soon as hecomes - I mean, you can find the menu anywhere, so decide what you want and don't go through the whole "here's-your-water-I'll-be-back" bit. And as you're finishing whatever your last course is, let him know you'll be ready to go in a minute so he knows to be ready to scan your magic band. If you're paying with a credit card, just hand it to him and tell him to run it. No need for the "I'll-leave-the-check-here-then-come-back" bit, either.
There is so much wasted time at the beginning and end of sit-down meals (anywhere, not just Disney).